The Nuclear and Industrial Safety Agency will revise regulations on coolant water pipes at nuclear plants and write a guideline in the wake of Japan's deadliest atomic plant accident, agency officials said Wednesday.

Currently, there is no guideline or standard on how, which parts and how frequently the pipes for the so-called secondary coolant water must be checked. Nuclear plant operators are only required to report to the government the results of annual inspections.

In Monday's accident at the Mihama Nuclear Power Plant in Fukui Prefecture, four workers were killed and seven were injured by superheated steam escaping from a ruptured pipe. The plant's operator, Kansai Electric Power Co., failed to inspect the pipe during the 27 years since the reactor began service in December 1976.